JP2005167247A - Preparing method of substrate, measuring method, device manufacturing method, lithographic device, computer program and substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved and desirable, more correct or convenient method for measuring the orientation of a crystal axis in a substrate. <P>SOLUTION: A plurality of markers are printed in resist on the substrate in an angle range to the crystal axis of the substrate. The markers are etched on the substrate using anisotropic etching process, the markers are those such that their apparent positions after they are etched depend on their orientation to the crystal axis. The apparent positions of the markers are measured, thereby the orientation of the crystal axis is derived. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for preparing a substrate, a measuring method, a device manufacturing method, a lithographic apparatus, a computer program for controlling the lithographic apparatus, and a substrate.

  A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a situation, a patterning means such as a mask can be used to generate a circuit pattern corresponding to the individual layers of the IC, which pattern comprises a substrate (layer) of radiation sensitive material (resist). For example, it can be imaged onto a target portion (eg comprising part of one or several dies) on a silicon wafer. In general, a single substrate will contain a network of adjacent target portions that are successively exposed. A known lithographic apparatus includes a so-called stepper in which each target portion is irradiated by exposing the entire pattern onto the target portion at one time, and each target portion has a projection beam in a predetermined direction ("scanning" direction). A so-called scanner that is illuminated by scanning the pattern through, while synchronously scanning the substrate parallel or antiparallel to this direction.

  Some devices made by lithographic techniques, such as devices that include optical waveguides, need to be accurately aligned with the crystal structure of the substrate on which they are built. In conventional silicon wafers, the flat portion is formed by cleaving the silicon crystal before it is cut into the wafer, thus giving an indication of the crystal axis. In a wafer having a notch rather than a flat portion, the position of the notch indicates the orientation of the crystal axis. However, both the flat part and the notch only indicate the {110} crystal axis within ± 1 °, which is insufficient for many applications. GaAs {011} and InP {011} wafers are generally specified with a tolerance of ± 0.5 °, but again more accurate alignment is often necessary.

  Techniques for determining the crystal orientation of Si and InP substrates by anisotropic etching of patterns are described in G. Ensell's Sens. Actuators A, 53, 345 (1996), M.M. Vangbo, Y. et al. Backlund, J.A. Micromech. Microeng, 6, 279 (1996), J. MoI. M.M. Lai, W.H. H. Chieng, YC. Huang, J.H. Micromech. Microeng, 8, 327 (1998), and M.M. Vangbo, A.M. Richard, M.C. Katlsson, K.M. Hjort, Electrochemical and Solid-State Letters, 2 (8) 407 (1999). However, none of these documents describes a methodology that can be easily automated and the results directly given to the manufacturing process.

  It is an object of the present invention to provide an improved and preferred more accurate or convenient method of measuring the orientation of the crystal axis of a substrate.

  According to an aspect of the present invention, there is provided a method for preparing a substrate, the method comprising providing a plurality of alignment markers each at a predetermined location on the surface of the substrate, The different alignment markers have different orientations with respect to the crystal axis of the substrate, and the form of the alignment markers is such that the apparent position of the alignment markers depends on their orientation with respect to the crystal axis. .

By printing a plurality of markers of different orientation on the substrate whose apparent position depends on their orientation relative to the crystal axis, a quick and accurate determination of the orientation of the crystal axis is known in the known accurate alignment system Can be performed using. In particular, an alignment system incorporated in the lithographic apparatus can be used. The orientation of the alignment marker preferably spans the expected range of change of the crystal axis orientation and a slight direction on either side, eg between 0.5 ° and 2 ° on either side of the nominal orientation of the crystal axis. The spacing between orientations should be sufficient to give enough data points for insertion and error averaging, for example to give a desired accuracy measurement, and the orientation of the alignment marker is (5 × It can be different from each other in an amount ranging from 10 ⁻⁶ ) ° to 4 °. The minimum increment of angle can be determined by the minimum rotation step of the substrate table of the lithographic apparatus used to print and / or measure the marker.

  According to a preferred embodiment of the present invention, the orientation dependence of the marker position is provided by etching the alignment marker on the substrate using an anisotropic etching process.

According to a further aspect of the present invention, there is provided a method for determining an orientation of a crystal structure of a substrate, wherein the substrate is provided with a plurality of alignment markers at predetermined positions on each of the substrates, The method wherein the different alignment markers have different orientations relative to the crystal axis of the substrate, the method comprising:
Measuring the position of the plurality of alignment markers;
Determining a deviation of the measured position of the alignment marker from the predetermined position;
Determining an orientation of the crystal axis with respect to the plurality of alignment markers from the deviation.

  This method can be used with the substrate of the first aspect of the present invention to obtain the desired measurement of crystal axis orientation.

  The measurement of crystal axis orientation can be performed at different times and possibly elsewhere, in which case the desired orientation indication information on the substrate and / or on another substrate cut from the same crystal It is desirable to make an entry in the database representing the determined orientation.

A further aspect of the present invention provides a device manufacturing method comprising:
Providing a substrate;
Providing a projection beam of radiation using an illumination system;
Using a patterning means to impart a pattern to the cross section of the projection beam;
Projecting a patterned beam of radiation onto a target portion of a substrate;
During the projection, the orientation of the substrate relative to the projected pattern is determined at least in part by referring to information indicative of the orientation of the crystal axis determined by the method described above.

  Thus, a structure whose function depends on or is improved by the correct orientation relative to the crystal axis of the substrate can be properly aligned with the crystal axis. In this way, the marker from which the orientation of the crystal axis is obtained can be provided on the opposite side of the substrate than the device to be manufactured. Also, the information indicating the orientation of the crystal axis can be derived from measurements of different substrates cut from the same single crystal.

  The alignment marker can take the form of any standard marker such as, for example, a lattice, a group of lattices, a chevron, or a box. Sensitivity to orientation can be provided by including in each marker at least one region having multiple small elements on a contrasting background.

  Furthermore, the present invention provides a lithographic apparatus configured to perform the above-described method and a computer program that directs the lithographic apparatus to perform the method of the present invention.

  Although the use of a lithographic apparatus in the manufacture of an IC may be specifically referred to herein, the lithographic apparatus described herein includes an integrated optical system, a guide and detection pattern for a magnetic domain memory, a liquid crystal display. It should be understood that other fields of application such as (LCD), thin film magnetic heads can be included. In the context of such other applications, all use of the terms “wafer” or “die” herein may be considered synonymous with the more general terms “substrate” or “target portion”, respectively. Those skilled in the art will understand what can be done. The substrate referred to herein may be processed before or after exposure, for example in a track (generally a tool for applying a layer of resist to the substrate or developing the exposed resist), or a metrology or inspection tool Can do. Where applicable, the disclosure herein may be applied to such substrate processing tools or other substrate processing tools. In addition, the substrate can be processed more than once, for example to make a multi-layer IC, so the term substrate used herein can also refer to a substrate that already contains multiple processed layers. it can.

  As used herein, the terms “radiation” and “beam” refer to ultraviolet (UV) radiation (eg, having a wavelength of 365, 248, 193, 157, or 126 nm), and extreme ultraviolet (EUV) radiation (eg, And all types of electromagnetic radiation, including particle beams such as ion beams or electron beams.

  As used herein, the term “patterning means” is broadly interpreted as referring to a means that can be used to provide a pattern to a cross section of a projection beam, such as forming a pattern on a target portion of a substrate. Should be. Note that the pattern imparted to the projection beam may correspond exactly to the desired pattern of the target portion of the substrate. In general, the pattern imparted to the projection beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

  The patterning means can be transmissive or reflective. Examples of patterning means include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include binary, Levenson type phase shifts, and halftone type phase shifts, as well as various types of hybrid masks. An example of a programmable mirror array uses a matrix configuration of small mirrors, where each small mirror can be individually tilted to reflect the incoming radiation beam in a different direction, and in this way The patterned beam is patterned. In each example of patterning means, the support structure may be, for example, a frame or a table that may be fixed or movable when required to ensure that the patterning means is at a desired position, for example with respect to the projection system. Can be. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning means”.

  As used herein, the term “projection system” refers to refractive optics, reflective optics, and the like, as appropriate with respect to other factors such as, for example, the use of exposure radiation or immersion fluid used, or the use of a vacuum. It should be broadly interpreted as encompassing various types of projection systems, including catadioptric optics. Any use of the term “lens” herein may be considered as synonymous with the more general term “projection system”.

  The illumination system can also include various types of optical components, including refractive, reflective, and catadioptric optical components for directing, forming, or controlling the projection beam of radiation, such components being In the following, they may also be referred to collectively or singly as “lenses”.

  The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a “multi-stage” machine, additional tables can be used in parallel, or one or more other tables can be used for exposure by one or more preparatory steps. Can be run on multiple tables.

  The lithographic apparatus may be of a type in which the substrate is immersed in a liquid having a relatively high refractive index, such as water, so as to fill a space between the final element of the projection system and the substrate. Immersion liquids can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the final element of the projection system. Immersion techniques are well known in the prior art for increasing the numerical aperture of projection systems.

  Embodiments of the invention will now be described by way of example with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts.

FIG. 1 schematically depicts a lithographic apparatus according to a particular embodiment of the invention. The device
An illumination system (illuminator) IL for providing a projection beam PB of radiation (eg UV radiation or DUV radiation);
A first support structure (e.g. a mask) that supports the patterning means (e.g. mask) MA and is connected to a first placement means PM for accurately placing the pattern formation means relative to the item PL.・ Table) MT,
A substrate table (e.g. wafer table) WT holding a substrate (e.g. resist-coated wafer) W and connected to a second placement means PW for accurately placing the substrate relative to the item PL When,
A projection system (eg a refractive projection lens) PL for imaging a pattern imparted to the projection beam PB by the patterning means MA on a target portion C (eg comprising one or more dies) of the substrate W. Prepare.

  As shown herein, the apparatus is transmissive (eg, using a transmissive mask). Alternatively, the device can be reflective (eg, using a programmable mirror array as mentioned above).

  The illuminator IL receives a beam of radiation from an irradiation source SO. The source and the lithographic apparatus can be separate, for example when the source is an excimer laser. In such a case, the radiation source is not considered to form part of the lithographic apparatus, and the radiation beam is removed from the source SO, for example by means of a beam delivery system BD with suitable directing mirrors and / or beam expanders. Pass to illuminator IL. In other cases, the radiation source may be an integral part of the device, for example when the radiation source is a mercury lamp. The radiation source SO and the illuminator IL, together with the beam delivery system BD if necessary, can be referred to as a radiation system.

  The illuminator IL may comprise adjusting means AM for adjusting the angular intensity distribution of the beam. In general, at least the outer and / or inner radial extent (commonly referred to as σ outer and σ inner, respectively) of the intensity distribution at the pupil plane of the illuminator can be adjusted. Furthermore, the illuminator IL generally comprises various other components such as an integrator IN and a capacitor CO. The illuminator provides a beam of conditioned radiation called the projection beam PB that has the desired uniformity and intensity distribution in its cross section.

  The projection beam PB is incident on the mask MA, which is held on the mask table MT. Across the mask MA, the projection beam PB passes through a lens PL that focuses the beam onto a target portion C of the substrate W. By means of the second placement means PW and the position sensor IF (eg interferometer device), the substrate table WT can be accurately moved, for example to place different target portions C in the path of the beam PB. Similarly, the first positioning means PM and other position sensors (not explicitly shown in FIG. 1) are in the path of the beam PB, eg after mechanical removal from the mask library or during scanning. On the other hand, it can be used to accurately position the mask MA. In general, the movement of the object tables MT and WT is realized by a long stroke module (coarse arrangement) and a short stroke module (fine arrangement) which form part of the arrangement means PM and PW. However, in the case of a stepper (as opposed to a scanner) the mask table MT can only be connected to a short stroke actuator or can be fixed. Mask MA and substrate W are aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

The apparatus shown can be used in the following preferred modes:
1. In step mode, the mask table MT and the substrate table WT are essential while the entire pattern imparted to the projection beam is projected once onto the target portion C (ie, a single static exposure). Remain stationary. The substrate table WT is then shifted in the X and / or Y direction so that different target portions C can be exposed. In step mode, the maximum size of the exposure area limits the size of the target portion C imaged with a single static exposure.
2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the projection beam is projected onto the target portion C (ie, a single dynamic exposure). . The speed and direction of the substrate table WT relative to the mask table MT is determined by the enlargement (reduction) and image reversal characteristics of the projection system PL. In scan mode, the maximum size of the exposure area limits the width of the target portion (in the non-scan direction) in a single dynamic exposure, while the length of the scan movement is the height of the target portion (scan direction). In).
3. In other modes, the mask table MT remains essentially static with programmable patterning means, and the substrate table WT projects the pattern imparted to the projection beam onto the target portion C. In between, it is moved or scanned. In this mode, a pulsed radiation source is generally used and the programmable patterning means is updated as necessary after each movement of the substrate table WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography using programmable patterning means, such as a programmable mirror array as described above.

  Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

  FIG. 2 shows an alignment marker 1 based on the standard form of the mark but modified for use in the present invention. As can be seen in FIG. 2, the alignment marker 1 comprises four quadrants 11 to 14 each having a lattice structure. Two quadrants 11 and 14 having these grid lines are aligned in the first horizontal direction in the figure, and the other two quadrants 12 and 13 having grid lines are in the orthogonal direction perpendicular to the figure. Aligned. The lattice lines in quadrants 11 and 14 are modified from the standard form to allow measurement of crystal axis orientation.

  As shown in FIG. 3, which is an enlarged view of a part of the line structure of the quadrant 11, the lattice spacing p includes a three-part structure of a solid region 15, an open region, and a stripe region 16. The stripe region has a large number of lines, four in this embodiment, but more or less can also be used, and the line width and pitch can be about 16 μm than the pitch of the grating. Pretty small. In general, the critical dimension of the orientation sensitive portion of the marker is preferably as small as printable with the lithographic apparatus used to print the marker. This marker can be made sensitive to its orientation relative to the crystal axis of the substrate by etching the marker in the substrate using an anisotropic etch step. In such an etching step, the substrate is preferably etched in a specific direction, eg parallel to the {001} crystal axis, compared to the vertical direction. When the marker is aligned in the preferred etching direction, the orientation-sensitive (striped) portion of the marker etches more strongly when the marker is at an angle relative to that direction so that the marker's center of gravity is shifted. Is done. How this effect is achieved is shown in FIGS. 4A to 4E.

  4A-4E show the resulting cross-section of the structure when the resist is exposed to the substrate at various different angles with respect to the crystal axis and then etched into the substrate in an anisotropic etching process. Show. The details of the anisotropic etch procedure determine the exact angle at which the structure is etched and the exact form of the structure that is etched at different angles. As shown in FIG. 4A, if the marker is at a large positive angle with respect to the crystal axis, the stripe region lines are completely etched away and the marker consists only of a solid portion. When the position of the marker is measured, the result is centered on the solid area as indicated by the arrow. If the marker is at a small angle with respect to the crystal axis as in FIG. 4B, the stripe line appears at the etched marker but decreases in width. The measured position with respect to the marker centroid is overshifted as indicated by the arrows. When the marker is accurately aligned with the crystal axis as in FIG. 4C, the stripe region appears completely in the etched structure, and the measured position displacement is maximum. The effect is the same for negative angles, as shown in FIGS. The same effect is achieved with other types of markers using regions that are also striped or have other sub-resolution divisions.

  FIG. 5 shows a wafer W in which the method of the invention is used to find the orientation of the crystal axis CA. The wafer W has a flat part F, which is nominally perpendicular to the crystal axis CA, but in practice the crystal axis CA is at an angle of ± 1 ° from the normal to the flat part. There is a possibility of coming off with R. (The predetermined angle and size NB of the markers in FIG. 5 are exaggerated for clarity.)

P _{+ n} of a series of alignment markers P _-n (shown are in FIG. 5 by the arrow) is exposed on the resist on the substrate at different angles r _n relative to the normal to the flat portion F as described above The The angle of the markers P _-n to P _{+ n} should span the possible angular range of the crystal axis C, preferably should exceed the possible angular range of the crystal axis C, and a sufficient number for insertion There should be a sufficient number to provide data points and average out the errors. The marker is preferably exposed under the same conditions, and preferably under optimal conditions for correct imaging of the stripe portion of the marker (or other relevant variables are excluded later in the method). The marker can be exposed in a single exposure with the appropriate marker containing the images of all markers at each angle, or the substrate can be rotated appropriately for each imaging step to produce a single marker image. Can be exposed in a separate exposure using a mask having The markers are preferably printed close together to minimize any position-dependent effects in imaging, and in any extra space on the substrate if the substrate is used for device manufacture. Can be printed. The markers need not be placed in a specific or consistent relationship between their position and their orientation relative to the normal to the flat portion F, but their relative positions are known with appropriate accuracy. It must be done. If the global position marker is already printed on the substrate or printed simultaneously, the predetermined position of the marker for the determination of the crystal axis is preferably known with respect to the global position marker.

The resist is then developed in the usual manner and the alignment markers P- _n to P _{+ n} are etched into the substrate in an anisotropic etching process. The exact etching process depends on the material of the substrate, and an appropriate process is known for common substrate materials. For example, a suitable anisotropic etch process for a silicon substrate is a KOH etch, whose process conditions, particularly temperature, can be optimized to maximize the etch direction selectivity.

In order to determine the orientation of the crystal axis CA, the absolute positions of the etched markers P _−n to P _{+ n} are measured using a standard alignment tool, for example an alignment tool incorporated in the lithographic projection apparatus, Their displacement d from their predicted position is determined. The alignment scan can be performed on a substrate table that is appropriately rotated so that the scan is exactly perpendicular to the marker. As described above, when the orientation of the alignment mark is closer to the crystal axis CA, the stripe portion is etched more intensely, and thus its center of gravity is more displaced and measured from the exposed nominal position. Causes a greater displacement of position. Therefore, the marker with the largest apparent displacement can be used as an indication of crystal axis orientation. However, for higher accuracy, all marker displacements can be considered. For example, the displacement d can fit two straight lines, with increasing angles to the normal to the flat part, one straight line going up and the other straight line going down, and the crystal axis orientation is now shown in FIG. As determined from the intersection of two straight lines.

  Once the orientation of the crystal axis relative to the flat part is known, this value can be taken into account in the manufacture of devices on the substrate. In particular, its function is (if the orientation of one crystal axis is known, of course, determining the other orientation is a subject of simple geometry) or depends on precise alignment with other crystal axes Or devices that are improved with accurate alignment can be accurately placed on the device. Accurate positions can be achieved using known crystal axis orientations in order to properly place global position (zero level) markers on the substrate, or these positions are already fixed. If so, the crystal axis orientation can be carried forward as a correction factor applied after alignment to the global position marker.

  It will be understood that the steps of the present invention need not be performed simultaneously or at the same location. For example, a series of markers can be exposed and etched at the time of manufacturing the substrate and at the manufacturing site, while obvious displacement measurements and offset value determination are performed when the device is exposed on the substrate. Can be done. This has the advantage that a high-precision alignment system in the presence of the lithographic apparatus is used for manufacturing, as if all steps are performed during device manufacturing. Also, if the substrate is not removed from the substrate table between the measurement of crystal axis offset and the printing of the entire position mark, the possibility of error using a flat part as a reference is avoided.

  However, all steps up to the manufacture of the device, for example the determination of the orientation of the crystal axes, away from the time of the substrate manufacturer can also be carried out. In this case, it is particularly convenient to take advantage of the fact that notches in the case of flat parts, or flat wafers, are generally made before a separate substrate is cut from a single crystal. Thus, all wafers cut from one crystal have the same orientation of the crystal axis relative to the flat portion (or notch). Thus, the measurements of the present invention can be performed on one (or perhaps a sample to minimize error) substrate cut from a given crystal, and then the results are all of the cut from that crystal. Applied to the substrate. Measurement results derived from individual or batch measurements can be marked in a machine or human readable form on a substrate or a data carrier to be bound, or in a database for retrieval when the substrate is in use. Can be entered.

  If the markers used in the method of the invention occupy an undesirable amount of space on the substrate, the markers can be placed on the opposite side of the substrate relative to the side used in the manufacture of the device. Of course, when applied after wafer reversal, the offset value must be changed in sign. In certain situations, it is also possible to remove the marker after it has been used in the method of the present invention.

  In certain cases, the present invention can be implemented in the form of a software upgrade to an existing apparatus, and thus the code executed by the supervisory control system of the lithographic apparatus, and the method of the present invention in a lithographic apparatus. It can be provided in the form of a computer program including instructions for executing the steps.

  While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.

1 shows a lithographic apparatus that can be used in embodiments of the invention. Fig. 4 shows a modified alignment marker that can be used in an embodiment of the present invention. FIG. 3 is an enlarged view of a part of the line structure of the alignment marker in FIG. 2. FIGS. 3A to 3E are views showing the action of etching the alignment marker of FIG. 2 at different angles. It is a top view of the board | substrate by the Example of this invention. It is a graph of the apparent position with respect to an angle used in the Example of this invention.

Claims (15)

A method for preparing a substrate, comprising:
Providing a plurality of alignment markers at respective predetermined positions on the surface of the substrate, wherein different alignment markers in the alignment markers have different orientations relative to the crystal axis of the substrate, and the alignment The marker form is a method in which the apparent positions of the alignment markers depend on their orientation relative to the crystal axis. The method of claim 1, wherein the orientations of the alignment markers differ from each other by an amount in the range of (5 × 10 ⁻⁶ ) ° to 4 °.   The method of claim 1 or 2, wherein the plurality of alignment markers have orientations ranging from 0.5 ° to 2 ° on either side of the vertical orientation of the crystal axis.   4. The method of any one of claims 1-3, wherein providing the alignment marker comprises etching the alignment marker on the substrate using an anisotropic etching process. A method of determining an orientation of a crystal structure of a substrate, wherein the substrate is provided with a plurality of alignment markers at predetermined positions on the substrate, and different alignment markers in the alignment markers are defined on the substrate. Having different orientations relative to the crystal axis, the method comprising:
Measuring the position of the plurality of alignment markers;
Determining a deviation of the measured position of the alignment marker from the predetermined position;
Determining the orientation of the crystal axis relative to the plurality of alignment markers from the deviation.   The method according to claim 5, further comprising forming a marker that is information indicating the determined orientation on the substrate and / or another substrate cut from the same crystal.   7. A method according to claim 5 or 6, further comprising making an entry into a database representing the determined orientation. A device manufacturing method comprising:
Providing a substrate;
Providing a projection beam of radiation using an illumination system;
Using patterning means for imparting a pattern to the cross section of the projection beam;
Projecting the patterned beam of radiation onto a target portion of the substrate;
8. During the projection, the orientation of the substrate relative to the projected pattern is at least partly by referring to information indicative of the orientation of the crystal axis determined by the method of any one of claims 5-7. Characterized in that it is determined automatically.   The projection is directed onto the first side of the substrate, the substrate comprising a plurality of alignment markers on the second side of the substrate, each at a predetermined position, and different alignments among the alignment markers The method of claim 8, wherein the markers have different orientations relative to the crystal axis of the substrate.   The projection is directed to a first substrate, the information indicative of the orientation of the crystal axis is derived from measurements of a second substrate, and the first and second substrates are cut from the same single crystal. Item 9. The method according to Item 8.   11. A method according to any one of the preceding claims, wherein the alignment marker is selected from the group consisting of a grid, a group of grids, a chevron and a box.   12. A method according to any one of the preceding claims, wherein each alignment marker comprises at least one region having a plurality of small elements on a contrasting background. A lithographic apparatus comprising:
An illumination system for providing a projection beam of radiation;
A support structure that supports patterning means that acts to impart a pattern to the cross-section of the projection beam;
A substrate table for holding the substrate;
A projection system for projecting a patterned beam onto a target portion of the substrate;
An alignment system for measuring the position of the alignment mark on the substrate;
A lithographic apparatus, wherein the control means controls the apparatus to perform the method according to any one of claims 5 to 10.   A computer program comprising program code means for instructing the apparatus to perform the method according to any one of claims 5 to 10 when executed in a lithographic apparatus.   A substrate having a plurality of alignment markers on each of them in a predetermined position, wherein different alignment markers in the alignment markers have different orientations with respect to the crystal axis of the substrate, and the form of the alignment marker A substrate in which the apparent positions of the alignment markers depend on their orientation relative to the crystal axis.